1. Field of the Invention
The present invention relates to an erecting equal-magnification lens array plate used in image reading devices and image forming devices.
2. Description of the Related Art
Some image reading devices such as scanners are known to use erecting equal-magnification optics. Erecting equal-magnification optics are capable of reducing the size of devices better than reduction optics. In the case of image reading devices, an erecting equal-magnification optical system comprises a linear light source, an erecting equal-magnification lens array, and a linear image sensor.
In the related art, a rod lens array capable of forming an erect equal-magnification image is used as an erecting equal-magnification lens array in an erecting equal-magnification optical system. Recently, however, there is proposed an erecting equal-magnification lens array plate comprising a stack of two transparent lens array plates built such that the optical axes of individual convex lenses are aligned, where each transparent lens array plate includes a systematic arrangement of micro-convex lenses on both surfaces of the plate. Since an erecting equal-magnification lens array plate such as this comprises a stack of lens array plates that can be formed by, for example, injection molding, an erecting equal-magnification lens array can be manufactured at a relatively low cost.
An erecting equal-magnification lens array plate lacks a wall for beam isolation between adjacent lenses. Therefore, there is a problem in that a light beam diagonally incident on an erecting equal-magnification lens array plate travels diagonally inside the plate and enters an adjacent convex lens, creating noise (referred to as ghost) as it leaves the plate. Light that does not contribute to imaging and that forms ghost is called stray light.
In one relate-art measure to address stray light, a light shielding member is provided to sandwich two lens array plates and a light shielding member is provided between the two lens array plates (see, for example, patent document No. 1). A through hole is provided in each light shielding member to pass imaging light.
[patent document No. 1] JP2011-17840
In a system where a stack of two of lens array plates and three light shielding members is built so as to form an erecting equal-magnification lens array plate, optical performance (resolution, in-plane distribution of resolution, stray light shield) as designed may not be obtained unless the optical axis of the convex lenses of the lens array plates and the central axes of the through holes are aligned.